Schizophrenia and/or bipolar disorder: the neurocognitive endophenotypes

Although Kraepelinian dichotomous conceptualization of psychosis was historically beneficial, modern studies do not support the existence of a sub-typing of psychotic illnesses into schizophrenic and affective psychoses. Years of intensive investigation on the genetic bases of schizophrenia and bipolar disorder suggest that these disorders, rather than being wholly distinct disorders, share common genetic risks. However, one of the most serious difficulties for genetic research in these illnesses is their enormous phenotypic heterogeneity. A response to this problem is the use of neurocognitive functions as endophenotypes or intermediate phenotypes. A review of the literature suggests that in both schizophrenia and bipolar disorder, neurocognitive functions are influenced by genetic factors and that there exists neuropsychological deficits in the nonaffected relatives of probands. However, it is unclear whether or not patterns of performance on neurocognitive tasks across probands as well as unaffected family members offer potential for identifying shared and illness-specific neurocognitive phenotypes for schizophrenia and bipolar disorder. Overlapping and unique neurocognitive endophenotypic signatures of the two psychoses are comprehensively described. (C) L'Encephale, Paris, 2012